The present invention relates to a rotary switch with direction-of-rotation output for use in electronic equipment.
One of the trends in portable electronic equipment, particularly cellular telephones, is to decrease the overall size of the device while increasing functionality. For example, the size of cellular telephones has decreased significantly from relatively large handheld units to devices no larger than a common pager while the number of functions that can be performed has increased dramatically. One problem associated with the reduced physical size involves engineering the user interface so that all the functions can be accessed in a reasonably efficient way. In addition to various keypad-type switches, rotary thumbwheel/push-button switches have been used. With a thumbwheel switch, a user merely rotates the thumbwheel in one direction or the other to call-up successive screen displays (i.e., a menu) and then pushes the thumbwheel along its axis of rotation to call a particular function presented on the screen. These thumbwheel/push-button switches offer substantial functionality while allowing one-hand operation of the device.
In a known switch of this type, the thumbwheel is connected to two sets of make/break switch contacts so that rotation of the thumbwheel will cause the two sets of switch contacts to open and close with one contact set leading or trailing the other by a selected phase difference (i.e., 90 degrees) as a function of the direction of rotation. Because the phase difference between the two switch outputs determines the direction of rotation, a program-controlled microprocessor must effect a quadrature analysis of the switch outputs to determine direction of rotation.
As can be appreciated, the use of a microprocessor dedicated to determining the direction of thumbwheel rotation results in a relatively expensive device.